Jamie Zigelbaum, a former student at MIT Media Lab, created a computer interface that takes the shape of an eyedropper.

Slurp is tangible interface for manipulating abstract digital information as if it were water. Taking the form of an eyedropper, Slurp can extract (slurp up) and inject (squirt out) pointers to digital objects. We have created Slurp to explore the use of physical metaphor, feedback, and affordances in tangible interface design when working with abstract digital media types. Our goal is to privilege spatial relationships between devices and people while providing new physical manipulation techniques for ubiquitous computing environments.

See also the 2003 MERL paper “Low Cost Sensing and Communication using Bidirectional LEDs”

The describe “iDropper” which is an incredibly simplified version of Slurp – the really beautiful part is that rather than using a whole passel of components, it simply uses an MCU and ONE LED for communication at about 30bps, which is plenty fast enough for very very small datagrams.